By Javier Velasco Montes - The Conversation
If there is a cosmopolitan and universal bacterium, it is Helicobacter pylori (H. pylori): it can affect people from all over the world and of all ages, although it is more common and is acquired earlier in less developed countries.
Half of the world's population is believed to be infected by it, no less.
In some cases, it can persist and cause disease in the stomach and duodenum. And, incredible as it may seem, despite being so widespread, we still know very little about how it is transmitted.
A special bacterium
These gastric microorganisms were first observed more than 100 years ago, and their link to gastritis became evident in the 1970s. Marshall and Warren identified and cultured in 1982 the stomach bacterium Campyobacter pyloridis, which was later classified as Helicobacter pylori.
This bacterium has special characteristics that allow it to survive in a very hostile environment such as the stomach and thus produce some diseases. It has been linked to chronic gastritis, many ulcers and stomach cancer, as well as lymphoma.
Little is known about the transmission
It is not known exactly how H. pylori infection is transmitted, although it probably occurs through fecal-oral or oral-oral exposure between different people.
Humans appear to be the main reservoirs of H. pylori, although it has also been found in captive primates and domestic cats. The latter may have viable bacteria in their saliva and gastric juice, which they could transmit to humans.
Sheep can also harbor H. pylori in their milk and gastric juice, which may explain why shepherds are infected more often than their offspring.
Fecal-oral transmission is also possible. The use of contaminated water in less developed countries can serve as an environmental source of the bacteria. H. pylori can persist in water for several days, allowing us to find traces of it in water in areas where infection is common.
Children who swim in rivers, streams, pools, or eat uncooked vegetables can be more easily infected. The bacteria has also been found in the feces of African children, where by the age of five almost all of the inhabitants are infected.
The more siblings, the more infections
The clustering of infections in some families suggests the possibility of human-to-human transmission. For example, spouses with H. pylori are more likely to infect their family members (spouses and children) than uninfected spouses.
A study conducted in Colombia found that the risk of infection was related to the number of children between two and nine years of age living in the same household. It was even shown that younger children were infected more often when older children in the same household were also infected.
Genetically identical H. pylori colonies have been isolated from people in the same family and those living within the same institution, suggesting the possibility of transmission between people living together.
In addition to familial transmission that occurs in developed countries, it can also occur between unrelated people living in countries with a high frequency of infection.
Helicobacter in dental plaque
Oral-oral transmission of the bacteria could not be confirmed, although it has been identified in dental plaque. However, dentists and dental hygienists who are exposed by their work do not get H. pylori infection more often. It is also known that infected gastric secretions can be a source of transmission of this bacterium.
Different medical devices, such as endoscopes and their accessories, can transmit H. pylori after contact with them Digestive doctors and nurses may be at higher risk of becoming infected, which could occur from exposure to infected gastric secretions during their work.
To reduce this risk of accidental or occupational transmission, they must be properly disinfected after use with patients.
Hereditary susceptibility
Hereditary susceptibility to H. pylori infection has not been demonstrated, although individuals of some ethnicities and races are infected more frequently than others. These differences are not fully explained by the social or economic differences between them.
The possibility of susceptibility to infection is also pointed out in studies done on twins. Thus, those who have grown up together have a higher infection concordance than those who have grown up separately. Therefore, the role of the environment during childhood appears to be important in the acquisition of H. pylori.
More studies needed
Not much is yet known about H. pylori, a bacterium that needs more research to know how we can prevent its transmission.
The fecal-oral and oral-oral routes between different people appear to be the most likely forms of transmission, although this is not yet clearly known. Luckily, once the infection is cured, a new one is not common.
This low rate of reinfection supports the existence of a lower risk of acquiring this bacterium during adult life. Immunity acquired after the first infection can also be important.